The spectral efficiency of LTE may be increased through the simultaneous transmission of cooperative multi point (CoMP) and carrier aggregation (CA) targeting. Carrier aggregation (CA) allows the combination of two or more carrier channels into an aggregated channel, thus enabling higher throughput as well as more efficient use of the highly fragmented LTE spectrum. A carrier aggregation configuration is defined as a set of one or more operating bands across which the BS aggregates carriers with a specific set of parameters. CoMP is a DL/UL orthogonalization technique to improve system capacity and cell edge user throughput. Currently, there are two different approaches for CoMP techniques. One approach is a decentralized autonomous control based on an independent eNB architecture, and the other is a centralized control based on remote radio equipment (RRE) architecture, which is also known as remote radio head (RRH).
There are practical benefits of simultaneously supporting CoMP and CA. For example, a macro eNB (evolved node B) may be deployed with a first component carrier (CC) while remote radio heads (RRHs) may be deployed with a second CC. For the user equipment (UE) at the cell-edge, between two RRHs, it is possible to benefit from the utilizing CoMP and CA simultaneously by configuring different transmission modes (TMs) on each of the CCs. Further, where two CCs are deployed in each of two macrocells, both CoMP and CA may be deployed and potentially COMP transmission for a UE at a cell-edge between two macro cells, e.g., transmission mode (TM) 10 may be deployed on both of CCs, wherein TM 10 provides non-codebook-based precoding supporting up to eight layers (suitable for CoMP), TM9 may be used to support transmission up to 8 layers from a cell, while TM10 supports CoMP transmissions from one or more cells. CoMP transmission can be signaled to the UE with a combination of semi-static Radio Resource Control (RRC) signaling and dynamic signaling through a physical downlink control channel (PDCCH).
Different transmission modes may be applied to downlink signals depending on what use the transmission mode makes of transmit diversity, spatial multiplexing, cyclic delay diversity (CDD), etc. Downlink channel quality is assessed at the UE and may be reported via the channel state information (CSI) Information Element (IE). The PUCCH (physical uplink control channel) is used to carry CSI (channel state information) reports regarding channel conditions, which allow a transmission point, e.g., an eNB, to dynamically adjust the downlink signal to the varying propagating and interference conditions.
Accordingly, the transmission modes and schemes, as well as the PUCCH CSI configurations, for different CCs may be independently configured and may well be very different in terms of, for example, periodicity. A collision between two or more CSI reports of different “CSI report sets” with the same set of PUCCH reporting instances is hard to mitigate without very stringent scheduler restrictions. For example, a periodic CSI collision may happen when the periodicity of one CC is a multiple of the other one, e.g., 10 ms and 40 ms, and the configured offset is the same. A periodic CSI collision may also occur when the periodicity of one CC is not a multiple of the other one, e.g., 20 ms and 32 ms, and for certain configured offsets.
A CSIProcessIndex is used to identify multiple CSI processes within a given CC. In order to support the feedback configuration and reporting for simultaneous CA and CoMP, a ServCellIndex is included to indicate the configured CC. The CSIProcessIndex is a parameter that is used for the CSI dropping rules in a CoMP scenario in case of collision between CSI reports of different serving cells with PUCCH reporting type of the same priority. Thus, a CSI dropping rule may be used for the scenario where TM 10 is configured for the CCs because the CSIProcessIndex is available for each serving cell with TM 10 configuration. However, the CSIProcessIndex is unspecified for legacy TMs (TMs 1-9) and thus handling CSI collisions for a hybrid TM case poses problems where a hybrid combination of legacy TMs and TM 10 is configured for CCs of one particular UE.